There are many applications where accurate detection of fluid flow is required. For example, in many medical devices the flow of body fluids, including blood, needs to be detected accurately. Some additional applications include infusion pumps, insulin pumps, enteral feed pumps, and wound irrigations systems, among others. Often, it is critical that any air bubbles or interference with fluid flow, such as by occlusions, within the conduit or tube must be quickly and accurately detected.
Different systems have been incorporated in medical devices to detect bubbles in a fluid stream. Often, ultrasonic energy is used to detect bubbles in fluid flowing in a tube. One such device is disclosed in U.S. Pat. No. 4,607,520 entitled “Method and Apparatus for Detecting Discontinuity in a Fluid Stream”, and issuing to Dam on Aug. 26, 1986. Therein disclosed is a device for detecting discontinuities such as air bubbles in a fluid stream. A tube containing the fluid stream is positioned between a transducer transmitting ultrasonic energy and a receiver receiving the transmitted ultrasonic energy upon passing through the tube and fluid stream. Signal processing circuits detect any modification of the ultrasonic energy indicating a discontinuity or bubble within the fluid stream. While this device is suitable for detecting bubbles or discontinuities in a fluid stream, it is not able to detect whether or not an occlusion or restriction to the flow of the fluid exists or that there has been a reduction in the fluid flow.
Other devices have been used to optically detect pressure changes in a tube that may be indicative of an occlusion or other restriction in the fluid flow. One such device is disclosed in U.S. Pat. No. 7,121,143 entitled “Optical Pressure Monitoring System” and issuing to Malmstrom et al on Oct. 17, 2006. Therein disclosed is a tube placed between an optical signal emitter and an optical signal receiver. The tube is formed from a generally elastomeric material, such as silicone. Accordingly any occlusion or viscosity increase will increase pressure, causing the tube to expand and move a portion of the tube between the optical signal emitter and the optical signal receiver which is optically detected. While this device is acceptable in many applications for detecting occlusions or a change in the fluid flow, it requires an optical signal emitter and an optical signal receiver to be placed on either side of the tube, making the device relatively large and difficult to implement efficiently in different applications.
In many applications both the detection of bubbles and the detection of fluid flow or changed due to an occlusion is necessary. This is especially applicable in medical devices used to monitor and detect blood flow. One such device is disclosed in U.S. Pat. No. 6,773,412 entitled “User Interface for Blood Treatment Device”, issuing to O'Mahony et al on Aug. 10, 2004. Therein disclosed is a renal replacement therapy device using fluid lines, pumps and sensors used for renal replacement therapy. Separate blood pressure sensors are used as well as an air detector circuit using ultrasound waves in a fluid to detect air bubbles in the blood passage. Use of these multiple, separate sensors, that are relatively large and cumbersome, make it difficult to develop small devices.
Accordingly, there is an increasing need for providing small, compact, easily transported or disposable devices in the medical field that can accurately and easily detect fluid flow and bubble. Therefore there is a need to produce easily manufactured sensors that can incorporate multiple functions in a single device and in a compact package.